Marker lights don't work, turn signals do?

Since the Road crews are migrating from a salt on the roads. To a liquid de-icer,(airports used it for years on planes)

It has a very nasty effect on copper connectors in wire, bulb and switches.

During the spring and summer I spend a month changing (corroded wire/connectors)

You can ask any O/O about wire corrosion has increased rapidly over the recent years past.

 

Wouldn't the obvious place to start be the light cord? I mean it worked before you unplugged it.

 

Wires are likely to be loose inside from pulling on the cord instead of the handle. Always start at the last thing done before the problem.

 

First thing I would do is unplug light cord from trailer and see what happens. This will narrow it down to either tractor or trailer. If still shorting out unplug the cord from the tractor side to see if cord is shorting out.

 

What make truck is it? If it has circuit breakers instead of fuses it could have a weak circuit breaker that needs to be replaced.

 

If everything except the taillights are briefly lighting up, the problem is in the taillights or the wiring to them. Go back there an wiggle stuff around by hand, you might find it that way.